January 25, 2000

Mapping the Earth, Swath by Swath

By WARREN E. LEARY

WASHINGTON, Jan. 24 -- In an ambitious move to better understand the ups and
downs of Earth, the space shuttle Endeavour is to make a detailed radar map of the
planet's surface that could be a boon to
everyone from military planners to weekend backpackers.

Endeavour and a six-member crew are to
be launched next Monday on an 11-day
mission to sweep most of Earth's land
masses with radar signals and create the
most complete, three-dimensional map of
the planet's surface ever assembled.

The mission is to gather so much data
about the hills, plains, valleys and other
surface details of planet topography that it
will take more than a year of analysis to
produce the global map. To retrieve information needed for the three-dimensional
views, the shuttle will have to extend a 197-foot metal and plastic antenna mast, the
longest rigid structure ever deployed in
space.

Scientists say comprehensive information
about height variations on land will aid
studies of erosion, flooding, earthquakes,
volcanoes, landslides and climate change. In
addition, it will improve maps used for land
and forest management, recreation and the
selection of sites for development, including
the placement of communications equipment like wireless telephone towers.

Topographical information from ground
and air surveys, and from radar data gathered by aircraft and space satellites, is
available for most parts of the world in
varying degrees of detail. But because information gathered at different times from
disparate sources is often hard to use in
research, scientists say the shuttle data will
be invaluable because it will be consistent
for the whole world. Spacecraft sent to
Venus and Mars have produced better topographical maps of those worlds than exist
for Earth.

In addition to topographical maps showing the elevations and depths of the surface,
the radar scans are to produce black and
white images of most of the planet's surface
area that are unobscured by clouds, fog or
darkness. Scientists say this picture mosaic
covering almost all of the populated area of
Earth will serve as an unprecedented reference point from which to study future
changes on the planet's surface.

"It will be a snapshot of the planet in one
10-day period," said Dr. Michael Kobrick of
NASA's Jet Propulsion Laboratory, the
chief scientist of the project. "There is
nothing else like it."

Endeavour is to fly in an orbit between 60
degrees North and 56 degrees South that
allows it to map all the land from the
southern edge of Greenland to the
southern tip of South America, an
area encompassing 80 percent of
Earth's land mass and 95 percent of
its population.

Originally set to fly last September, the mission was delayed while
NASA inspected the entire four-shuttle fleet for electrical wiring problems. Inspections and subsequent repairs were ordered after the shuttle
Columbia suffered an electrical
short that knocked out two engine
computers during its launching in
July.

The radar mapping flight was
delayed again when NASA decided to
launch the shuttle Discovery ahead
of it in December to repair the Hubble Space Telescope.

Researchers involved with the
mapping flight were surprised, and
some were disturbed, by a decision
last week by mission managers to
reduce the number of days of radar
mapping to 9 from 10.

Paul Dye of NASA's Johnson
Space Center in Houston, the lead
flight director for the mission, said
officials had decided to cut data
gathering short to improve the
chances of retracting and saving the
long antenna mast in case problems
developed at the end of the mission.
Earlier plans called for severing the
expandable mast from the shuttle
and discarding it in space if problems developed in retrieving it. The
new schedule gives astronauts time
to perform an emergency spacewalk
to help reel in the mast.

Although there are currently no
plans to fly the radar equipment and
mast again, Mr. Dye said managers
wanted to keep future options open.
The mast is also very similar to long
trusses that will be deployed from
the International Space Station to
support its solar power arrays, and
some experts said NASA might wish
to re-examine one that had been used
in space.

"We decided it was a good idea to
preserve the mast, to keep the capability to bring the mast in," Mr. Dye
said. "This is a device which we've
never deployed before."

Dr. Kobrick, disappointed that scientists would lose 10 percent of their
expected data, said, "I wish it were
otherwise." He said the research
team was looking into alternatives
for getting the lost data, including
the somewhat unlikely possibility of
extending the mission for a day by
conserving power aboard the shuttle.
The radar equipment uses so much
power that some officials believe this
is improbable.

Another issue raised by the mission is who will have access to the
information it gathers.

A major co-sponsor of the mission,
contributing $200 million toward its
cost, is the Defense Department's
National Imagery and Mapping
Agency, which provides maps and
pictures to military and civilian intelligence agencies. The military
agency said it would restrict availability to the mission's most detailed
mapping data for national security
reasons.

Military applications for this information include improved weapons
targeting, better aircraft navigation
and flight simulator training, and
enhanced battlefield management
and tactical planning.

The radar mission will produce
highly detailed data in so-called 30-meter resolution, about three times
more detailed than 90-meter data
commonly available for most parts
of the world. This resolution will provide three-dimensional information
in an area about 100 feet on each side
that has a vertical height accuracy of
at least 16 meters (about 50 feet) and
down to 6 meters (20 feet) in the best
case.

The military agency said it would
make worldwide 90-meter data
available to anyone who wanted it, as
well as 30-meter data for the United
States, where information of this detail is already commonly accessible.
However, it said, 30-meter information for the rest of the world would be
restricted and available to civilian
researchers only on a case-by-case
basis. Agency spokesmen have questioned whether civilian users need
the detailed map data.

Dr. Victor R. Baker, a professor of
hydrology and water resources at
the University of Arizona, said his
research on flooding and the flow of
rocks and other debris along waterways was improved by having the
most detailed topographical information available. "We can do a better job if we have 30-meter data,
particularly if it's digital and can be
combined with other kinds of data,
such as imagery," he said, "But even
having 90-meter data helps if it is
from the same source."

Dr. Baker said most of his research concerned the United States,
where 30-meter data from the shuttle
mission was expected to be available. "But having the same data
available for places elsewhere would
help us compare similar features
and enhance our work," he said.

Dr. Kobrick of NASA said he saw
little difficulty working under his
agency's arrangement with the Defense Department about the data.
"The 30-meter data will be available,
but I will have to ask for it," he said,
"Their only request is that I don't
publish the raw data itself with my
results. I'm perfectly happy with this
arrangement we have."

Thomas A. Hennig, the military
agency's program manager for the
project, pointed out that only about
60 to 70 percent of the world was now
mapped at 90-meter resolution and in
some places, even this is restricted
information. Releasing data of this
resolution for the world, along with
the radar image mosaic, amounts to
a huge increase in topographical information benefiting people worldwide, he said.

John E. Pike, a space and military
policy expert with the Federation of
American Scientists, said the military agency had legitimate concerns
about releasing the detailed data.
"This information is potentially useful to other militaries, also," he said,
"The Defense Department wants to
see that the data doesn't fall into
hostile hands."

Space shuttles have flown radar-mapping instruments on five previous occasions, culminating in two
flights in 1994 that demonstrated
three-dimensional mapping by flying
over the area twice to take slightly
offset images that were later combined into pictures showing elevation
differences. Dr. Kobrick and Edward
Caro, an engineer also with the Jet
Propulsion Laboratory, came up
with the idea of getting three-dimensional topographical images from
the shuttle in a single pass by putting
additional radar receivers on a boom
extending from the spacecraft.

Once Endeavour reaches orbit, it
is to deploy the boom almost immediately from a canister in its cargo
bay.

Flying with modifications to the
same equipment used in 1994, Endeavour is to orbit 145 miles above
Earth, making radar scans in swaths
140 miles wide. The international
mission features radar equipment
made by the German Space Agency
and the Italian Space Agency.

The shuttle, flying upside-down
and tail first, will sweep the path
with C-Band and X-Band signals
transmitted by antennas that are
part of its 29,000-pound cargo of radar equipment. The signals will
bounce off Earth and back to the
shuttle, where they will be picked up
by receiving antennas in the cargo
bay and at the end of the 640-pound
mast almost 200 feet away.

Using a technique called interferometry, each antenna will record almost identical data to form images,
but the offset distance will cause
slight phase variations in the signal
that allow creation of three-dimensional images when the data is combined. NASA said the scans would
produce so much data that it would
take more than 13,500 standard CD-ROM disks to contain it.